This invention relates to nonvolatile memory, and more particularly to a cross point structure utilizing electric pulse induced resistance change effects in magnetoresistive films.
Materials having a perovskite structure, among them colossal magnetoresistance (CMR) materials and high temperature superconductivity (HTSC) materials are materials that have electrical resistance characteristics that can be changed by external influences.
For instance, the properties of materials having perovskite structures, especially for CMR and HTSC materials, can be modified by applying one or more short electrical pulses to a thin film or bulk material. The electric field strength or electric current density from the pulse, or pulses, is sufficient to switch the physical state of the materials so as to modify the properties of the material. The pulse is of low enough energy so as not to destroy, or significantly damage, the material. Multiple pulses may be applied to the material to produce incremental changes in properties of the material. One of the properties that can be changed is the resistance of the material. The change may be at least partially reversible using pulses of opposite polarity from those used to induce the initial change.
Accordingly, a memory structure is provided, which comprises a substrate, a plurality of bottom electrodes overlying the substrate, a plurality of top electrodes overlying the bottom electrodes forming a cross point memory structure. A perovskite material located at each cross point interposed between a top electrode and a bottom electrode, wherein the perovskite material acts as a bit. Each bit may act as a variable resistor within a memory circuit.
A low cross talk memory structure is formed by depositing and patterning a conductive material over a substrate to form at least one bottom electrode. A layer of insulating material, such as silicon dioxide, is deposited over the substrate and the at least one bottom electrode. At least one contact opening is etched through the insulating material to the underlying bottom electrode. A layer of perovskite material is deposited over the bottom electrode and the insulating material. The perovskite material is polished off of the surface of the insulating material so that perovskite material remains in the contact opening. At least one top electrode is formed such that it crosses over the bottom electrode at the position of the perovskite material forming a cross point.
A memory circuit may be formed on the substrate prior to formation of the memory structure. The memory circuit assists with the programming and read out of the memory structure. Forming the memory circuit prior to the memory structure reduces damage to the perovskite material due to additional subsequent processing following formation of the memory structure.